The present invention relates to a contactless communication device and a contactless IC card which are used for electronic money, transportation ticket gates, and the like, and particularly to a technique effectively applied to e.g. a semiconductor device for an IC card.
According to the international standard ISO/IEC 14443 and ISO/IEC 18092, an IC card having a contactless interface is called a PICC and performs RF (Radio Frequency) communication with a reader/writer called a PCD. ISO stands for the International Organization for Standardization, and IEC stands for the International Electrical Commission. PICC stands for Proximity Card, and PCD stands for Proximity Coupling Device.
Transmission data from the PCD to the PICC is defined as “downstream data”, and transmission data from the PICC to the PCD is defined as “upstream data”. The common sequence of contactless communication is that the PICC receives downstream data from the PCD, performs internal processing, and transmits upstream data to the PCD in response to the downstream data. Repetition of the downstream data and the upstream data enables contactless communication.
In recent years, with the diversification of applications, the internal processing time (transaction time) of the PICC has been steadily increasing.
In the internal processing by the PICC, the processing time can be decreased with increasing processing speed. That is, the increase of the processing speed of the PICC enables various processes during the period between reception and transmission by the PICC. However, the consumption current of the PICC increases with the increase in the internal processing speed of the PICC. Since the power to the PICC is generated, by electromagnetic induction, from carrier waves supplied from the PCD, the communication distance for allowing contactless communication decreases with the increase in the consumption current of the PICC. Although it is possible to increase the communication distance by decreasing the consumption current of the PICC, it is necessary to decrease the internal processing speed of the PICC in order to decrease the consumption current. That is, the consumption current and processing speed of the PICC have a trade-off relationship, and the communication distance for allowing contactless communication and the processing speed have a trade-off relationship.
A contactless communication device applied to the PICC rectifies a signal inputted from an antenna terminal and supplies a direct current obtained by rectification to a regulator to generate a predetermined level of source voltage. According to WO2003/091819 (Patent Document 1), if it is determined that a direct current flowing through a voltage regulation unit as the regulator is not less than a predetermined current, control is performed so that a specific circuit such as a coprocessor can operate. According to Japanese Unexamined Patent Publication No. 2005-191961 (Patent Document 2), an operation clock frequency in an IC card is controlled in accordance with the relative magnitude relationship between a power level received by the IC card and a power level consumed in the IC card. For example, if a power level consumed in a semiconductor integrated circuit is less than the received power level by a predetermined amount, the operation clock frequency is increased. In the reverse case, the operation clock frequency is decreased. According to Japanese Unexamined Patent Publication No. 2006-119693 (Patent Document 3), the received voltage of a signal inputted to an antenna terminal is referred to for monitoring of the received energy, and by comparing the margin of the received energy with a control rule, a required processing speed is calculated to control the processing speed of a logic unit, thereby ensuring compatibility between the securing of a contactless communication distance and high-speed processing.